The invention relates to apparatus for sealing and cutting shrink-wrap film material for use with a shrink-wrap machine for individually wrapping articles and, more particularly, to a multi-stage shrink-wrap sealing and cutting apparatus for use with a shrink-wrap machine.
Shrink-wrap machines for packaging articles with shrink-wrap film material generally include a loading station at which articles are sequentially loaded onto the machine, and propelled by a conveyor through a wrapping station which wraps articles sequentially with shrink-wrap film material from a film supply. The conveyor carries articles wrapped in the film material to a film sealing and cutting station, the design of which may vary with the desired type of seal that is to be applied. For example, if film is folded around the periphery of an article, and the opposing edges of the film material overlap and extend to one side of the article, one commonly used seal is a side seal. In producing a side seal, opposing surfaces of the film material are bonded together by application of heat and pressure along the peripheral surfaces of a single roller pair situated on opposing sides of the film material as the film-wrapped articles are sequentially passed along that portion of the machine. Due to the geometry of the roller pair, which comprises two adjacent circular rollers, the heat and pressure applied to opposing sides of the film material occurs only at the relative point of tangency between the peripheral surfaces of the roller pair. The term xe2x80x9crelative point of tangencyxe2x80x9d is used because, of course, the film material passes between the peripheral surfaces of the roller pair.
In addition to forming a seal along the opposing surfaces of film material, it is generally desirable to trim as much excess overlapping film from the package to be formed. A package refers to the film-wrapped article that has been completely processed by the shrink-wrap machine and is ready for retail sale. Conventionally, both the sealing and trimming operations have been performed by the same single pair of rollers. This may be accomplished by one roller having a peripheral surface which includes opposing beveled edges which form a cutting edge that extends along the peripheral surface. The other roller may have a substantially flat peripheral surface, but be comprised of a somewhat resilient material, such as a hard rubber, to more conformally receive the cutting edge of the other roller.
In operation, the film material passes between the opposing surfaces of the roller pair. At the relative point of tangency between the peripheral surfaces of the opposing roller pairs, the cutting surface cuts through the film material. Simultaneously, as the film material is being cut, a seal is formed along the edge of the film material adjacent the cut line by the combined heat and pressure between the peripheral surface of the inside beveled edge of one roller and the flat peripheral surface of the other roller.
After this combined trim seal and cutting operation are performed, the film-wrapped articles are further carried along the shrink-wrap machine. Subsequently, a cutting and sealing operation places a transverse seal between adjacent articles thus creating individually wrapped film-wrapped articles. Finally, the film-wrapped articles are processed through a heating station which causes the shrink-wrap material to shrink with respect to the articles, at which point the film-wrapped articles become packages.
Machines of this character are generally operated at high-speed, to maximize their efficiency. Therefore, the highest operational speed the machine can attain is limited by the operation which takes the machine the most time to perform. The availability of newer shrink-wrap materials are playing a more critical role in such efficiency considerations.
A class of very strong new heat-sealable film materials (referred to herein as the xe2x80x9ctough film materialsxe2x80x9d or the xe2x80x9cnew tough film materialsxe2x80x9d), such a Cryovac(copyright) CorTuff(trademark) made by Sealed Air Corporation, is being increasingly used in industry to wrap articles. Packages of such tough film materials are extremely strong and tough, providing very high impact and cutting protection. They are strong enough and sufficiently protective that they can function as primary shipping containers without more, and may be used as an alternative to corrugated boxes. Use of such materials provides substantial savings and packaging and shipping cost reductions. However, these new tough film materials are far more difficult to cut and seal than conventional shrink-wrap film materials.
Conventional cutting and sealing apparatus previously described which both form and cut film material, as by using a single roller pair, may only be able to operate at 40 percent or even less of its maximum operating speed previously attainable with conventional shrink-wrap film materials, if at all. These tough film materials require additional heat to form a seal of acceptable strength between opposing surfaces of shrink-wrap film material. Due to such need for increased heat, a single roller pair design is no longer sufficient, especially if higher operating speeds are required, as there are limits to the amount of thermal energy that can be effectively conducted to film material at a single tangential region of contact between heated and pressurized surface peripheries associated with a single roller pair. However, the use of multiple stages which may comprise at least one set of roller pairs selectably heated to establish a side seal, followed by at least one set of rollers to cut the film material, permits these higher operating speeds to be attained. An analogy may be found in rocket boosters, where a main booster rocket is required to put a payload into a speed and/or altitude from which the payload rocket can proceed at high speed to ultimate trajectory. It is accordingly desired that multiple stages of roller pairs be provided for a film sealing and cutting apparatus that are selectively heatable to permit high-speed operation of a shrink-wrap machine.
Among the several objects, features and advantages of the present invention may be noted an improved film sealing and cutting apparatus for use with a shrink-wrap machine for individually wrapping articles which:
achieves extremely high-speed and throughput;
achieves such wrapping when using tough film materials;
can be used for wrapping products when using difficultly sealable film materials such a Cryovac(copyright) CorTuff(trademark);
requires less film overlap around articles to be wrapped, thereby reducing material costs;
permits independent vertical adjustment of the roller pairs;
permits ease of separation between an opposing pair of guide chains;
permits the use of different thicknesses and composition of shrink-wrap film materials.
Briefly, according to a first embodiment, the present invention relates to an improved film sealing and cutting apparatus for use with a shrink-wrap machine for individually wrapping articles sequentially with shrink-wrap film material of different possible thickness and composition, and most especially new tough film materials heretofore applied with difficulty or slow throughput. The shrink-wrap machine includes a wrapping station at which articles are first wrapped with shrink-wrap film material from a film supply so that opposing edges of the film material overlap and extend to one side along the articles, but the film material is not yet sealed. A conveyor carries articles wrapped in the film material from the wrapping station to a film sealing and cutting station at which the film material is sealed and cut along one side of the articles as they move with respect to the film sealing and cutting station. According to this first embodiment, the new film sealing and cutting apparatus comprises at least a first and second pair of rollers. The first pair of rollers is in opposition to present peripheral surfaces of the rollers of the first pair in opposition for forming a seal between opposing surfaces of the film material along longitudinal edges thereof between the rollers of the first pair. A pressure-producing structure urges the rollers of the first pair in opposition toward each other. A heater causes heating of at least one of the rollers of the first pair, to form by heat and pressure between the peripheral surfaces of the rollers of the first pair. A longitudinal seal is thus produced by the first pair of rollers along a side of each article, as film-wrapped articles pass by the first pair of rollers. The second pair of rollers are in opposition in proximity to the first pair of rollers for engagement of the film material proximate the seal after formation thereof. At least one of the rollers of the second pair has a cutting periphery. Pressure-producing structure urges the rollers of the second pair in opposition toward each other, so as to cut by pressure applied to peripheral surfaces of the second pair of rollers through opposing surfaces of the sealed film material along the film material, and so leaving a margin between a cutting path formed by the peripheral surfaces of the second pair of rollers and the inside edge of the seal.
According to a second embodiment particularly beneficial in the sealing of the new tough film materials, the new film sealing and cutting apparatus includes two pairs of selectively heated rollers. Overlapping layers of film material wrapped around an article are passed on one side of the article between peripheral surfaces of each roller pair. The first roller pair forms a thermal conditioning pre-seal between opposing surfaces of the overlapping layers by application of heat and pressure along the peripheral surfaces of the first roller pair. The second roller pair then completes the seal and cuts through the opposing surfaces, leaving a margin between a cutting path formed by the peripheral surfaces of the second roller pair and the seal. Pressure-producing structure urges the respective roller pairs in opposition toward each other.
Other objects, features and advantages will be in part apparent and in part pointed hereinbelow.